Temperature-stable LC oscillators and methods of oscillation at temperature null phase

Abstract

An LC oscillator tank that generates a tank oscillation at a phase substantially equal to a temperature null phase. The oscillator further includes frequency stabilizer circuitry coupled to the LC oscillator tank to cause the LC oscillator tank to operate at the temperature null phase. In one aspect of the disclosure, a feedback loop may split the output voltage of the LC tank into two voltages having different phases, where each voltage is independently transformed into a current through programmable transconductors, The two currents may be combined to form a resultant current which is then applied to the LC tank. The phase of the resultant current is such that the LC tank operates at an impedance condition that achieves frequency stability across temperature.

Description

FIELD OF THE INVENTION[0001]The present invention generally relates to highly stable Inductor-Capacitor (LC) oscillators which utilize the LC tank temperature null phenomenon to minimize the variations of the oscillator output frequency.BACKGROUND OF THE INVENTION[0002]Electronic clock generation classically relies on a reference oscillator based on an external crystal that is optionally multiplied and / or divided to generate the required clock. The key specifications of a clock, other than its target frequency, are frequency accuracy and stability. Frequency accuracy is the ability to maintain the target frequency across supply and temperature and is usually represented as drift from the target frequency in percent or parts per million (ppm). Long term stability, is impacted by the close-in phase noise of the oscillator. An oscillator using a high-Q element typically has a low phase noise profile, and thus good frequency stability, and is less sensitive to variations in oscillator a...

AI Technical Summary

Benefits of technology

[0019]The present invention provides a substantially temperature-independent LC-based oscillator. The oscillator includes an LC oscillator tank and frequency stabilizer circuitry coupled to the LC oscillator tank to cause the LC oscillator tank to operate at a temperature null phase generating a tank oscillation at a phase substantially equal to a temperature null phase. The temperature null phase is a phase of the LC oscillator tank at which variations in frequency of an output oscillation of the oscillator with temperature changes are reduced or minimized.

[0020]For example, the feedback loop may split the output voltage of the LC tank into two voltages having different phases, where each voltage is independently transformed into a current through programmable transconductors. The two currents may be combined to form a resultant current which is then applied to the LC tank. The phase of the resultant current is adjusted such that the LC tank operates at an impedance condition that achieves frequency stability across temperature.

Problems solved by technology

Long term stability, is impacted by the close-in phase noise of the oscillator.

However, not all resonators, including crystals, have satisfactory performance across temperature, thus the need for extra circuitry and techniques to decrease and / or compensate for shifts in frequency due to temperature.

However, the ever increasing complexity of electronic systems due to requirements of supporting multiple standards, increased functionality, higher data rates and increased memory in a smaller size and at a lower cost is pushing designers to increase the integration level through the development of Systems on Chip (SoC) in deep submicron Complimentary MOS (CMOS) technologies to benefit from the increased gate density.

Reference clocks incorporating crystal oscillators have not managed to scale or integrate due to the bulky nature of crystals, thus limiting the size and cost reduction possible for electronic systems.

However, packaging induced stress and its impact on performance still remains as a challenging obstacle, since the high-Q element may require special packages and / or calibration that are not practical for SoCs.

The stress may change the temperature behavior of the resonator, possibly resulting in large frequency shifts and accelerated aging.

Therefore, special assembly and packaging techniques are typically required to mitigate such effects, which increase the cost of producing such clocks.

Similar problems may be encountered by any resonator that is dependent on the mechanical properties of the resonator material, which require careful design and manufacturing procedures and processes.

However, the reported frequency accuracy of these implementations suffers from large drift across supply and temperature, making them ineffective for applications requiring precise accuracy and stability.

A mitigation to reduce the drift across temperature requires trimming across temperature which is neither cost effective nor practical for SoCs.

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